This invention relates to optically readable data storage media and, more particularly, to techniques to render said media unreadable after being read at least once.
It is often desirable when distributing software or other information that is recorded on a medium to insure that only one party is enabled to read the recorded information. For example, a company that sells computer software will find it advantageous to enable only the purchaser to read the software from a disk and transfer or install the software to computer memory, such as a hard disk, while preventing subsequent access by other parties to the software. However, this has proven to be a vexing problem that is not readily solved.
When the information is distributed on a read/write medium, such as the ubiquitous floppy disk, it may be possible to cause the installation software to erase all or part of the information after it has been successfully installed. Unfortunately, such information may be distributed on write-protected disks, thereby rendering such erasure impossible. Also, any protection mechanism that relies on computer software to implement has the potential to be defeated by additional computer software.
U.S. Pat. No. 5,815,484 discloses an optical disk having a reflective metallic layer with a plurality of data structures (pits and lands) and a reactive compound superimposed over at least some of the data structures. The reactive compound is a photochromic compound which changes from an optically transparent condition to an optically opaque condition when subjected to readout light and/or atmospheric oxygen. The darkening of the photochromic compound prevents a sufficient amount of readout light from being detected by the readout apparatus, thereby effectively rendering the optical disk unreadable.
At least one perceived disadvantage of this approach is that photochromic darkening is often reversible, which could be used to defeat the technique.
It is a first object and advantage of this invention to provide an improved system and method to render an optically readable media, such as, but not limited to, a laser disk, a compact disk (CD), or a digital video disk (DVD), unreadable.
It is a second object and advantage of this invention to provide an improved system and method to render an optically readable media permanently unreadable, after having been read at least once.
It is a third object and advantage of this invention to provide an optically activated mechanism that destroys or impairs the reflectivity of a metal-containing layer, thereby rendering an optically readable media unreadable.
It is a further object and advantage of this invention to provide an optically activated mechanism that modifies a transparent layer so as to cause readout beam aberration, thereby rendering an optically readable media unreadable.
It is once further object and advantage of this invention to provide a mechanism that relies on non-atmospheric oxygen, such as oxygen preloaded into or generated within a layer of an optically readable media, for modifying the optical properties of the media so as to render the media optically unreadable.
It is still another object and advantage of this invention to provide a mechanism that relies on an evaporative technique for modifying the optical properties of an optically readable media so as to render the media optically unreadable.
It is another object and advantage of this invention to provide a mechanism that alters a surface characteristic of an optically readable media so as to detrimentally affect a readout apparatus tracking process during an attempted readout of the media.
It is a further object and advantage of this invention to provide a mechanism that causes surface topography changes to an optically readable media so as to detrimentally affect a readout apparatus feedback and tracking process, thereby adversely affecting the fidelity of the readout.
The foregoing and other problems are overcome and the objects and the advantages of the invention are realized by methods and apparatus in accordance with embodiments of this invention.
In one aspect this invention provides a method for making an optically readable media unreadable during a play process. The method includes steps of (a) providing the media with an optically activated mechanism that degrades the reflectivity of a surface wherein information is encoded; (b) exposing the media to optical radiation for reading out the information; and, during the step of exposing, (c) initiating the operation of the optically activated mechanism. In this embodiment the step of initiating includes steps of (d) generating singlet oxygen in a layer disposed on the media; and (e) reacting the singlet oxygen with a metal-containing layer for oxidizing the surface of the metal-containing layer, thereby degrading the reflectivity of the surface. The step of generating may include a step of diffusing the singlet oxygen through a diffusion barrier that is disposed between the layer and the metal-containing layer.
In a further aspect the optically activated mechanism causes a defocusing of a readout beam, thereby degrading reflection of the readout beam from a surface wherein information is encoded.
In one embodiment the method generates an optical intensity gradient in a layer disposed on the media; and, in response to the generated gradient, deforms a surface of the layer resulting in readout beam aberration and/or adversely affecting the tracking process, resulting in readout degradation and a loss of fidelity. In this case the step of providing provides the layer so as to comprise an azobenzene-containing polymer. In an alternate embodiment a surface layer may react with an atmospheric component, such as oxygen, so as to degrade the tracking process by inducing a surface topography change, without inducing any significant change in the light transmission properties of the surface layer.
In another embodiment the step of initiating includes steps of: irradiating a photocurable polymer region that comprises part of the media; and, in response to the irradiation, photopolymerizing the polymer, thereby changing an index of refraction of the polymer resulting in readout beam aberration.
This invention also encompasses optically encoded media that operate in accordance with the foregoing methods, and that are constructed in accordance with the techniques of this invention.
In accordance with further embodiments of this invention an optically readable media has a patterned structure for encoding information that can be readout by application of light, and further includes a layer that is comprised of a volatile component and at least one other component. Removing at least some of volatile component by evaporation or sublimation causes an increase in at least one of photoabsorption or scattering with the remaining component, thereby rendering at least a portion of the encoded information unreadable. The other component can include a lactone dye, such as crystal violet lactone, and the volatile component can be, for example, NMP (N-methyl pyrrolidinone). In a further embodiment an organic material, such as CsF or KBr, is coated on the surface of the disk and provides a surface haze when exposed to water vapor or carbon dioxide, thereby increasing the scattering and decreasing the signal-to-nose ratio, and degrading the readout fidelity.
A method is disclosed for making an optically readable media unreadable. This method includes steps of (a) providing the media with a surface layer having a planar surface topography; and (b) subsequent to or during a first readout of the optically readable media, modifying at least a portion of the planar surface topography to a non-planar surface topography. This is accomplished by the use of at least one of a photoresponsive polymer, a removal of a substance from the surface layer to the atmosphere, or by interaction with a substance in the atmosphere. This latter process may occur without significantly modifying a transparency of the surface layer to a readout beam. The deviation of the non-planar surface layer topography from the planar surface layer topography is sufficient to detrimentally affect at least a tracking operation of a readout device that generates the readout beam.